Nylon melt-spinning apparatus



Sept. 13, 1966 M. s. KANBAR NYLCN MELT-SPINNING APPARATUS Filed May 27, 1963 /a frog/Ey United States Patent IO 3,271,817 NYLON MELT-SPINNING APPARATUS Maurice S. Kanbar, S E. 15th St., New York, N.Y. Filed May 27, 1963, Ser. No. 283,236 6 Claims. (Cl. 18-8) This invention relates generally to the melt-spinning of nylon, and more particularly to an improved technique and apparatus for the melt-spinning of nylon in an atmosphere of steam to produce nylon liber and yarn of superior quality.

For the most part, polyamide liber and yarn of the type commercially available, is based either on nylon 66 derived from hexamethylenediamine and adipic acid, or or nylon 6, derived from caprolacta-m. The conversion of nylon chi-ps or flakes into yiiber is effected by 4the meltspinning process wherein the melt is extruded through a spinneret to form laments which are then cooled and solidiiied. These filaments are subsequently drawn to orient their molecular structure, with a resultant increase in tensile strength.

The nylon flakes used in melt-spinning have a water con-tent determined by the amount of water remaining after polymer production, as well as the amount thereafter absorbed from the atmosphere. Since at elevated temperatures, the degree of depolymerization of polyamides in a 4function of the amount of water present, it has general-ly been the practice to dry the nylon iiakes so as to reduce the Water content before melt-spinning. Also, in the course of melt-spinning, dry nitrogen has been used to sweep away some of the water present during spinning. The need to pre-dry the iiakes and the equipment entailed when melt-spinning under a positive pressure of nitrogen, contributes substantially to processing costs.

To avoid the necessity of pre-drying nylon flakes and melting them in nitrogen atmosphere, it has been known t-o introduce steam into the'melting chamber, the steam serving to control the polymerization-depolymerization equilibrium, whereby yarn of good uniformity may be obtained. In apparatus yheretofore employed for this purpose, steam from an external boiler is introduced into a melt chamber having a heater grid, the steam serving to blanket the polymer and to adjust the viscosity of the melt in relation t-o the water vapor pressure of the steam. The advantage of the steam process is that it becomes possible to use an untreated polymer iiake having a moisture content as high as 6.75%, no special equipment being necessary either to precondition the flake or to melt it in an inert atmosphere. Thus substantial economies are effected in the melt-spinning process.

The difficulty with steam-operated melt processing apparatus of the prior-art type is that the Steam is intermingled with the unmelted flake, thereby slowing down the reaction time and delaying the establishment of the desired equilibrium. Moreover, since the steam is derived from an external source, this calls for a relatively elaborate system of pipes, thermal insulation and pressure control means.

Accordingly, it is the main object .of this invention t-o provide a melt-spinning process and apparatus wherein steam is generated Within the chamber rather than in an external source, the steam pressure being maintained at a desired level.

Also an object of the invention is to provide an apparatus of the above type wherein the nylon is introduced into the steam chamber in molten form to accelerate its in- 3 ,2 71,817 Patented Sept. 13, 1966 lCe teraction with steam and to attain equilibrium more quickly.

Another object of the invention is .to provide an apparatus of the above type wherein the melt pool in the chamber is maintained `at a constant level by regulating the melt input thereto. Since the nylon is introduced into the chamber in molten form, it is not necessary to heat the pool to as high a temperature as would be required in grid systems wherein the nylon enters in ake form.

A significant advantage of the invention is that spinning is carried out under a posi-tive water vapor pressure, the melt being spun under unvarying conditions of temperature, moisture and pressure to produce a yarn having uniform and optimum properties. It is important to bear in mind that if polymerization and de-polymerization is not in equilibrium, the resultant yarn varies in molecular weight and hence is non-uniform in tenacity and elongation. With the present invention, the various factors involved in the melt process are stabilized, and variations in the quality of the output are obviated.

Briefly stated, these objects are attained in an apparatus comprising a heated chamber wherein water is introduced into an evaporation pan, the Water being vaporized to :form steam whose pressure is maintained at a predetermined level by a relief valve which discharges steam from the chamber when the pressure level therein is exceeded, the steam reacting with the incoming stream of molten nylon which is fed into the chamberfthrough a melt extruder, thereby forming a melt pool in the chamber, from which pool the molten nylon passes through a metering pump into a spinne-ret which extrudes the nylon in lamentary form. The operation of the melt extruder is controlled as a function of the melt pool level whereby the supply of molten nylon into the chamber is regulated to maintain a substantially constant pool level.

Another drawback in existing steam-operated melt processing apparatus, is tha-t it is difficult to maintain the melt pool at a desired level relative to the steam in the chamber. The level of the pool in such `steam systems is to some degree controlled by the metering pump which governs the depletion rate at which the melt is forced through the spinneret, and hence the rate at which the level of the pool is lowered. The pool level may be raised by elevating the temperature of the grid, thereby melting more polymer. However, a rise in temperature will also 'bring about 4an increase in degradation of polymer. Generally the grid is designed t-o mel-t only enough to feed the amount of polymer that the pump is metering. This imposes a practical limitation on the system.

For example, if the grid is melting enough to make denier yarn and denier yarn is desired, one of two changes must be made to accomplish this result. Either -the speed of take-up must be out in half or the capacity of the grid to melt must be doubled. (The pump can be run at twice the speed, or a larger pump can be used.) Since changing the take-up speed presents ydiiliculties and raising the grid temperture in order to melt at a faster rate will degrade the polymer, the usual solution is to employ a grid of larger capacity.

In the present invention, the switch-over from 70 denier to 140 denier may be carried out more easily. Let us, for example, assume that the extruder used has a maximum capacity of 30 pounds per hour. If therefore 70 denier yarn is being made and taken -up at a constant speed of say 1800 feet per minute, about 5 pounds per hour will be needed; hence the extruder will be run at its slowest speed. If now we Wish to make 140 denier, all that need be done is to increase the extruder screw speed to produce pounds per hour and also double the speed of the metering pump or use a larger pump.

Obviously the screw melt system is much more flexible than the grid melt arrangement and carries out melting of the polymer at a much faster rate.

For a better understanding of the invention as well as other objects and further features thereof, reference is made to the following detailed description to be read in conjunction with the accompanying drawing, wherein the single figure schematically shows an apparatus in accordance with the invention.

Referring now to the drawing, the apparatus is constituted by two main components, namely a melt extruder, generally designated by numeral 10, and a melt spinning chamber generally designated by numeral 11. In t-he extruder 10, the polymer in chip or flake form is supplied to a hopper 12, from which it passes through the feed throat into the channel of the rotary screw conveyor 13 driven by a motor 14 through a gear reducer 14a. The barrel 15 of the conveyor is surrounded by suitable heating coils or bands 16, 17 and 18 which are preferably operated electrically and serve to raise the temperature within the barrel to a degree sufficient to melt the nylon flakes. The temperature is measured by a thermocouple 18a. As the granules are conveyed along the screw channel they are melted, the melt being forced through a melter plate 18h.

The output of the screw conveyor communicates with the chamber 11 and terminates in a spinneret 19, The direction of screw rotation is such as to convey the molten nylon in the direction of the spinneret, from which it is extruded in the form of a monoor multi-lament stream 20.

Chamber 11 is surrounded by heater bands 21, 22 and 23 which serve to heat the space therein to a degree maintaining the stream of nylon fed therein in the molten state, the stream collecting within the chamber to form a melt pool 24. Since the heat of the chamber is only that necessary to maintain the pool in a molten condition rather than to melt dry flakes as in prior arrangements, the chamber may be operated at a lower heat level with less ydegradation to polymer.

Also flowing into vthe chamber through a pipe 25 is a stream of water, preferably distilled, which is discharged within the chamber into a spreader-pan 26 positioned above the melt pool. The flow of water is adjusted by a valve 27 in the pipe line. The water received in the pan is quickly vaporized, the temperature in the chamber being well above 212 F. Thus steam is generated within the chamber, whereby the molten polymer in the pool is blanketed with an atmosphere of steam.

The amount of steam pressure within the chamber is regulated by a relief valve 28 of conventional design, which is set to discharge steam from the chamber when a predetermined pressure is exceeded. In practice, the pressure may be set at between 7 to 30 lpounds per square inch gauge. The pressure setting depends on such factors as the nature of the polyamide being spun and the type of yarn being formed, the higher the steam pressure the higher the amount of water in the melt in equilibrium with the steam, and the lower the viscosity of the melt.

In general, the invention is operable with any polyamide which includes the polyesteramides. T'he polymer flakes used may have a relatively high moisture content, in the order lof 4 to 7 percent, there being no need to precondition the akes before spinning.

Since the nylon enters the chamber in a molten stream and is immediately exposed to the steam atmosphere, the desired condition of equilibrium is rapidly attained. The molten polymer is metered out of the chamber through a metering pump 29 of any known construction, which passes the melt continuously and at a constant rate to the spinneret assembly 30, from which the nylon is extruded inthe usual filamentary form.

To prevent decomposition, the inventory of polymer in the melt should be as small 'as possible, but the amount should be sufficiently large so that the melt is exposed to the steam before being metered out to establish equilibrium. The height of the melt pool in the chamber is maintained substantially constant by means of a suitable probe 32 whose tip is slightly Iabove the desired level of the pool, such that if the pool touches the probe, a response -is produced by electrical, mechanical or optical means to operate a sensing relay 33 connected to the control circuit of motor 14. In this way the motor may be cut olf or its speed reduced when the pool goes above the desired level, to arrest or slow down the operation of the screw :conveyor until such time las the pool is lowered by operation of the metering pump 29. Thus a closed feedback loop is formed between the motor-controlled extruder and the melt pool, to stabilize the level of the pool.

Thus molten nylon is fed in the chamber and is withdrawn therefrom at relative rates maintaining a desired pool level w-hle the pool is subjected to steam pressure at a controlled level.

While there has been shown a preferred embodiment of nylon melt-spinning apparatus in accordance with the invention, it will be appreciated that many changes and modifications may be made therein without, however, departing from the essential spirit of the invention as dened in the annexed claims.

What is claimed is:

1. Apparatus for spinning polyamides, comprising:

(a) la melt extruder 'having a predetermined maximum capacity and including variable speed means to operate said extruder in :a range extending from a minimum rate to a rate in accordance with said predetermined maximum capacity, an input andan output,

(b) means to feed polyamide ake into the input of said extruder,

(c) means to heat the flake within said extruder to a temperature level sufficient to melt same whereby said polyamide emerges from the output of said extruder in molten form,

(d) la steam treatment chamber,

(e) means coupling the output of said extruder to said chamber to introduce a stream of molten polyamide `therein which collects as a melt pool,

(f) mans to feed water into said chamber above said (g) means to apply heat to said chamber at a temperature level maintaining the molten condition of said pool and vaporizing said water to form steam subjecting said pool to steam pressure,

(h) means to regulate said steam pressure in said chamber to maintain a predetermined steam pressure level therein,

(i) a spinneret, and

(j) a meter-ing pump intercoupling said `chamber With said spinneret to pass said molten polyamide therethrough to form polyamide filaments, said pump being operable at different rates, the highest of which removes less of said molten polyamide from said chamber than said melt extruder is capable of introducing therein at its maximum capacity.

2. Apparatus as set forth in claim 1, further including means to vary the feed of molten polymer into said chamber to maintain the pool at a desired level.

3. Apparatus as set forth in claim 1, wherein said vaporization means includes an evaporation pan to receive water fed into said chamber.

4. Apparatus as set forth in claim 1, wherein said means to maintain steam pressure at a desired level is constituted by a relief valve.

5. Apparatus as set forth in claim 1, wherein said conveyor is operated by a motor which is controlled as a function of the level of the pool in said chamber.

5 6 6. Apparatus as set forth in claim 5, further including 3,093,445 6/ 1963 Freeman 264-176 a probe to sense the level of the pool and means coupled 3,110,930 11/ 1963 Beck 18-8 to said probe to control motor operation. FOREIGN PATENTS I References Cited by the Examiner 5 628,935 10/1961 Canada.

UNITED STATES PATENTS 752,665 7/ 1956 Great Brltam.

2, 71, 7 1951 Wa tz Gayler H. Examlner.

2,747,224 5/1956 Koch et a1 264-176 l0 K. W. VERNON, L. S. SQUIRES, Assistant Examiners.

3,010,147 11/1961 Davies et al 264-176 

1. APPARATUS FOR SPINNING POLYAMIDES, COMPRISING: (A) A MELT EXTRUDER HAVING A PREDETERMINED MAXIMUM CAPACITY AND INCLUDING VARIABLE SPEED MEANS TO OPERATE SAID EXTRUDER IN A RANGE EXTENDING FROM A MINIMUM RATE TO A RATE IN ACCORDANCE WITH SAID PREDETERMINED MAXIMUM CAPACITY, AN INPUT AND AN OUTPUT, (B) MEANS TO FEED POLYAMIDE FLAKE INTO THE INPUT OF SAID EXTRUDER, (C) MEANS TO HEAT THE FLAKE WITHIN SAID EXTRUDER TO A TEMPERATURE LEVEL SUFFICIENT TO MELT SAME WHEREBY SAID POLYAMIDE EMERGES FROM THE OUTPUT OF SAID EXTRUDER IN MOLTEN FORM, (D) A STEAM TREATMENT CHAMBER, (E) MEANS COUPLING THE OUTPUT OF SAID EXTRUDER TO SAID CHAMBER TO INTRODUCE A STREAM OF MOLTEN POLYAMIDE THEREIN WHICH COLLECTS AS A MELT POOL, (F) MEANS TO FEED WATER INTO SAID CHAMBER ABOVE SAID POOLO (G) MEANS TO APPLY HEAT TO SAID CHAMBER AT A TEMPERATURE LEVEL MAINTAINING THE MOLTEN CONDITION OF SAID POOL AND VAPORIZING SAID WATER TO FORM STEAM SUBJECTING SAID POOL TO STEAM PRESSURE, (H) MEANS TO REGULATE SAID STEAM PRESSURE IN SAID CHAMBER TO MAINTAIN A PREDETERMINED STEAM PRESSURE LEVEL THEREIN, (I) A SPINNERET, AND (J) A METERING PUMP INTERCOUPLING SAID CHAMBER WITH SAID SPINNERET TO PASS SAID MOLTEN POLYAMIDE FROM SAID THROUGH TO FORM POLYAMIDE FILAMENTS, SAID PUMP BEING OPERABLE AT DIFFERENT RATES, THE HIGHEST OF WHICH REMOVES LESS OF SAID MOLTEN POLYAMIDE FROM SAID CHAMBER THAN SAID MELT EXTRUDER IS CAPABLE OF INTRODUCING THEREIN AT ITS MAXIMUM CAPACITY. 